I am a Plat III Tryndamere and Nasus main and have recently climbed from Bronze to Plat playing them both. I have a Tryndamere guide on mobafire too if you are interested in checking it out. I'm a top main and have only been playing for about a year. I have developed skill relatively fast and expect to reach plat very soon by playing nasus. If you are interested, here is my opgg.

My Tryndamere Guide.

If you have looked at other guides on Nasus, you will notice that the build and rune pages are very different. Why? This guide is meant for maximum carry potential. When you start snowballing, the conqueror and ghost combo is unstoppable. For SoloQ, this is the perfect build to climb with.

PROS
Nasus is a very strong champion once mastered. He has few mechanics which makes him a very good pick into soloQ. Lastly, he is a monster late game and is able to carry by either split pushing or front lining in team fights. If you are looking for a consistent carry in Low to Mid elo (Mid=High Diamond). Nasus is a great pick up and main.

CONS
Nasus is very strong in the late game, but his early game is horrendous. If punished hard enough, enemies could potentially make you useless and end in under 20 minutes. The main goal as Nasus is to not allow this to happen, as Nasus can easily 1v1 most laners past 25 minutes and start carrying. Lastly, although Nasus is very strong late game, he can still be kited very easily and shutdown without even getting a chance to start attacking the squishy targets.

EARLY GAME

Nasus is known for his weak early game. Your primary goal is to stack up your Q on minions. Avoid taking as many trades as possible and don't use your Q on champions, as it will slow down your stacking and it doesn't really do much damage anyway without stacks. Aim to have around 180 stacks by 10 minutes. After you have 180 stacks, sheen, and your ultimate, you should be able to all in the enemy laner unless they are ahead or playing safe (this almost never happens against a Nasus). Engage an all in with R>W>auto>E>Q>auto and then just continue to auto and Q them (mixing in W slows and E armor reduction when CDs are up) until they get away or die. Be careful though, if you all in when you aren't strong enough to beat them 1v1, you will set yourself very far behind and delay your impact on the game for a long time. Remember, your primary goal of laning phase is to get as many stacks as possible, but don't pass up opportunities to get kills.

P.S.
I normally aim for 400 stacks at 20 mins and 600 or higher at 30 minutes

MID TO LATE GAME

Outside of laning phase, you have two game plans, split pushing or team fighting.

Choose to Team Fight if...

1) You are ahead and your team is ahead.
2) You are behind and your team is behind

Choose to Split Push if...

1) You are ahead and your team is behind.
2) You are behind and your team is ahead

Team Fighting

Your role in a team fight is to front-line and neutralize the threat of the enemy adc. Always engage with your ult activated and try to get a W slow on the enemy adc. If you are extremely ahead, you might be able to flash on the adc and try to burst them down. If you cant get a W slow on the enemy adc, try to protect your own adc by standing by them and W slowing any enemy that tries to engage on them. Most of the time, you can start a fight if you catch out an enemy that tries to engage on the adc alone.

Split Pushing

Nasus is a great split pusher because his Q does MASSIVE damage to turrets when at high stacks and with a sheen proc. Also, he will be able to 1v1 almost every enemy laner with enough time, so he will draw enough pressure to force 2-3 players to come to the lane to contest you, allowing your team to have the #'s advantage. When split pushing, try to be as far away from the most important neutral objective at the time. So if baron is up, you will want to split push bot lane because if the enemy collapses on you your team can secure baron and they wont be able to contest the play. If baron is down, go top lane to allow your team to get dragon for free. Make sure to ward the jungle that you are split pushing toward to make sure you don't die for free and make your team lose 4v5 after you were caught. If you can't get objectives because you are behind, wait until you get enough stacks and gold and start team fighting off of the lead u got from splitting.

CORE


This item is built first item 90% of the time. It gives you a HUGE power spike and allows you to start winning lane. Not taking this item is a huge mistake, unless you decided to take Iceborn Gauntlet instead.


This item is an option instead of trinity force in games where you are doing terribly early game and can barely stack. This item does not give you as much of a power spike as Trinity Force, but it can help you get back into the game by stacking passively in a side lane.
BOOTS


This is my go to choice for boots because it helps you in negate time under cc in team fights, allowing you to do way more damage.


This is a pair of boots I pick when I plan on split pushing vs. an auto attacking laner or if they have many AD opponents on their team.
TANK ITEMS


This item is the most common tank item for Nasus, with or without magic damage enemies. The extra healing, CDR, and health help Nasus an INSANE amount in every situation. If you are facing a high magic damage team, you must build this item after your core. Even if you are facing 0 magic damage opponents, I still like to get this item after i get a few armor items.


This item is the most common armor item I take on Nasus. If you are facing a high AD comp or 2 or more auto attacking champions, this item is AMAZING as a second item (after Trinity Force). It gives you insane amounts of armor, mana, and most of all CDR. If you rush this second, it will give you 40% CDR and a large amount of tankiness that can make you unstoppable.


This item is very good if facing a comp that is heavily focused around magic damage. Normally would go Trinity Force into Spirit Visage into Adaptive Helm to reach 40% CDR and get tons of MR for a heavy AP comp.


This item is really good after you have already reached 40% CDR and are facing drain tanks/champions with lifesteal. This is a very efficient item for Nasus, so it will help you be tankier aswell as reduce the healing of their entire team.


This item is really good if you are facing a fed ADC. This is also the standard item for Nasus if no other armor item is inherently good at that moment. Just remember to use the active for the item and it will be a very effective choice in most situations.


P.S. The rest of the items are highly situational so if you want to know when to take them then look at the notes of the "Situational Tank Items" for info about when to get each of the items.